Dynamic fracturing by successive coseismic loadings leads to pulverization in active fault zones
Dynamic fracturing by successive coseismic loadings leads to pulverization in active fault zones
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DOI：
10.1002/2015jb012542
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发表时间：
2016-04
期刊：
影响因子：
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通讯作者：
F. Aben;M. Doan;T. Mitchell;R. Toussaint;T. Reuschlé;M. Fondriest;J. Gratier;François Renard
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文献类型：
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作者：
F. Aben;M. Doan;T. Mitchell;R. Toussaint;T. Reuschlé;M. Fondriest;J. Gratier;François Renard
先前的研究表明，在实验室中，只要应变率高于一定的粉碎阈值，沿着大断层观察到的岩石可以通过单次高应变率加载产生。这种载荷类似于大型地震事件。在现实中，粉状岩石受到了多次地震事件的影响，而不是一次地震事件。因此，通过施加低于初始粉碎阈值的加载条件，研究了连续的“温和”高应变率加载对粉碎阈值的影响。采用分离式霍普金森压杆装置对石英-二长土进行了单次和连续加载实验。通过施加增量应变来监测与损害相关的岩石物性和弹性模量。此外，研究还表明，在应变速率为~180 s−1至~90 s−1的情况下，连续施加“较温和”的动载荷可以降低粉化阈值。要做到这一点，岩石必须在粉碎前的连续加载过程中经历动态破裂。结合地震破裂时的荷载条件，将形成以下垂直于断层的广义断层破坏带结构：在离断裂面最远的地方，有一个静止的外边界，边界上有一个动态破碎的岩石带。在离断层更近的地方，一个粉状边界划定了一个粉状岩石带。连续的地震事件会使粉状岩石带逐渐变宽，最终形成成熟断层中观察到的更宽的破坏带。
Previous studies show that pulverized rocks observed along large faults can be created by single high‐strain rate loadings in the laboratory, provided that the strain rate is higher than a certain pulverization threshold. Such loadings are analogous to large seismic events. In reality, pulverized rocks have been subject to numerous seismic events rather than one single event. Therefore, the effect of successive “milder” high‐strain rate loadings on the pulverization threshold is investigated by applying loading conditions below the initial pulverization threshold. Single and successive loading experiments were performed on quartz‐monzonite using a Split Hopkinson Pressure Bar apparatus. Damage‐dependent petrophysical properties and elastic moduli were monitored by applying incremental strains. Furthermore, it is shown that the pulverization threshold can be reduced by successive “milder” dynamic loadings from strain rates of ~180 s−1 to ~90 s−1. To do so, it is imperative that the rock experiences dynamic fracturing during the successive loadings prior to pulverization. Combined with loading conditions during an earthquake rupture event, the following generalized fault damage zone structure perpendicular to the fault will develop: furthest from the fault plane, there is a stationary outer boundary that bounds a zone of dynamically fractured rocks. Closer to the fault, a pulverization boundary delimits a band of pulverized rock. Consecutive seismic events will cause progressive broadening of the band of pulverized rocks, eventually creating a wider damage zone observed in mature faults.